The present invention relates to a semiconductor diode. More particularly, the invention relates to semiconductor diodes which can be utilized in circuits that experience high voltages and currents.
A goal in the development of modem circuits is to reduce the number of required circuit components, such as capacitors or resistors. In particular, there is an attempt to reduce protective circuitry, which leads to increased loading of the components. Increased demands are thus placed on the loadability of these components with a sharp rise or fall in current or voltage.
Given rapid cut-off processes, a dynamic avalanche can occur in power diodes. This effect is brought about by holes (defector electrons) which flow to the anode through the space charge region which forms at the pn-junction. Given sufficiently large current densities, these charge carriers act as an additional doping of the semiconductor material in the area of the space charge region and can lead to the generation of additional charge carriers (avalanche effect). This occurs given electrical voltages which are far below the breakthrough voltage of the diode in the stationary operation. When the current flows through a component, the charge carriers diffuse from the active region in the edge region of the component. If a voltage applied in the forward direction is cut-off, the flowing of charge carriers present due to the diffusion process at the side of the p-emitter or the p-emitter contact can lead to increased current densities in the edge region by means of the terminal contacts. As a result, the component can be destroyed if the generation of charge carriers from the dynamic avalanche effect is too intense. This problem arises primarily when the n-emitter is larger or only negligibly smaller (i.e. by approximately the thickness of the component) than the p-emitter.
European Patent Document No. EP 0 262 356 B1 describes a method for producing a pn-junction of high voltage stability. In this example, the edge of a doped region constructed at the top surface of a semiconductor body has a boundary layer that forms a pn-junction. The pn-junction curves at the edge toward the top surface of the semiconductor body. The result is a gradually decreasing dopant concentration in an outward direction. To this end, a semiconductor layer is used on the top surface as a dopant source, and the dose of the in-diffusion of the dopant is progressively reduced, moving outward by a plurality of recesses of different widths which are etched out in this semiconductor layer.
U.S. Pat. No. 5,284,780 teaches a method for increasing the voltage stability of a semiconductor component with a plurality of layers of alternating conductivity types. With this method, the edge terminations of a pn-junction in a thyristor are irradiated with electrons in order to reduce the lifetime of the charge carriers in these regions. This reduces the current amplification in the edge region and increases the voltage stability of the component.
The present invention provides an improved power diode in semiconductor material that is suitable for use in circuits in which the diode is operated to the limits of its loading capacity.
To this end, in an embodiment of the present invention, a power diode includes a semiconductor body having a first surface, a second surface and a base doping for electrical conductivity. Two regions are doped with opposites signs for electrical conductivity. The first region is on the first surface and the second region is on the second surface. A first contact is on the first region and a second contact is on the second region. A third region is within the semiconductor body and has an outer section in which a reduction of the concentration of the dopant in the first region and/or an increasing of the concentration of recombination centers in the outer section lowers a charge carrier concentration in the outer section.
In an embodiment, the concentration of recombination centers in the outer region is increased by introducing a plurality of high energy particles into the outer region by irradiation.
In an embodiment, the concentration of recombination centers in the outer region is increased by introducing a numerous heavy-metal atoms into the outer region by irradiation.
In an embodiment, the first contact extends a predetermined distance across the first region, and the concentration of dopant in the first region is lower in two outer edge areas covered by the contact than the concentration of dopant in a middle area covered by the contact and extending between the two outer edge areas.
In an embodiment, the power diode has a thickness and the first contact has dimensions that are larger than the corresponding dimensions of the second contact by, at the most, the thickness of the power diode in every direction of the first surface.
In an embodiment, the second surface is longer than the first surface, the second contact extends across the entire second surface and the doping of the second region has a sign of conductivity that is the same as a conductivity of the base doping of the semiconductor body.
In an embodiment, concentration of dopant of the first region steadily decreases in a direction from the middle area to the two outer edge areas covered by the first contact.
In an embodiment, the concentration of dopant in the first and second regions is lower in an area covered by the respective first or second contacts and is positioned at the edge of the respective first or second contact than in a remaining area which is covered by the contact in the middle of the contact.
In an embodiment, an edge region is modified such that the dynamic avalanche effect described above is effectively suppressed or at least limited. The power diode has a structure of doped regions with a pn-junction in a semiconductor body. The pn-junction extends transversely to the main direction of the current path, which is defined by two regions which are doped for opposite signs of electrical charge. These regions are at the first surface and the second surface of a semiconductor body. The first and second surfaces each have a base doping with terminal contacts.
In the operation of the diode, the current flows through the semiconductor material essentially perpendicular to the first and second surfaces. At the edges of the current path, the inventive power diode is designed so that, in the on-state of the diode, the charge carrier concentration at the edge region is more sharply reduced than in the remaining area. Thus, given a cut-off of a current in the flow direction, high current levels resulting from charge carriers flowing off at the edges of the current path do not arise, particularly not in the region of the pn-junction beneath the edge of the p+-contact.
It is thereby inventively achieved that multiple recombination centers are introduced in the edge region, or that the charge carrier injection in the operation of the diode is reduced progressively in the direction of the edge in that the doping concentration of an n+-doped or a p+-doped region on which a contact is placed (n-emitter or p-emitter, respectively) decreases proceeding toward the edge. These means can also be present simultaneously.
These and other advantages and/or features of the present invention are described below in the following detailed description of the preferred embodiments with reference to the accompanying drawings.